Detection of White Spot Syndrome virus and Yellowhead virus in prawns imported into Australia.

OBJECTIVE To determine whether viable White Spot Syndrome virus (WSSV) or Yellowhead virus (YHV) were present in prawn products imported into Australia. PROCEDURE A sample of fourteen uncooked prawns was obtained from a consignment imported from southeast Asia. Each of the prawns was examined for WSSV by polymerase chain reaction (PCR), and then a bioassay was conducted in which a 10% homogenate of cuticular epithelium from each of the prawns was inoculated intramuscularly into healthy challenge prawns (Penaeus monodon) from Australia. The latter were then monitored for clinical signs of disease, and tissue samples were processed for electron microscopy, histological examination and for detection of WSSV by in situ hybridization (ISH) using a commercial kit. Limited numbers of haemolymph samples from inoculated challenge prawns were also examined by PCR for the presence of WSSV and YHV. All work was carried out under microbiologically secure conditions. RESULTS Results of the initial PCR examination for WSSV on the imported prawns were not definitive. However, in the bioassay, several of the challenge prawns inoculated with homogenates from the imported prawns showed clinical signs of disease (inappetence and lethargy) within 24 h post inoculation (pi) and died at 1 to 4 days pi. Tissue samples from a number of moribund prawns demonstrated lesions typical of White Spot Disease (WSD), and the presence of the virus was confirmed by electron microscopy, ISH and PCR. YHV was also demonstrated by PCR in two challenge prawns inoculated with homogenates. CONCLUSION Viable WSSV and YHV were present in frozen prawn products imported into Australia for human consumption from southeast Asia. Importation of frozen infected products may present a risk of transferring virus to wild and farmed populations of crustaceans in this country. To date, WSD and Yellowhead Disease remain exotic to Australia.